AVO Multimeter survey

[peterpixel]

Hi Ian, thanks for the response. Battery access is on the top of the meter and the Data Plate is a thin metal plate like the earlier ones. The address on the plate is Dover and it says "A Member of the Thorn Group" and Model 8. I now cannot remember when I obtained this it's so long ago but I've always believed it to be a MK III. Best of luck with your task. Peter.

[pmmunro]

The MkIII version of the Model 8 Avometer can be identified by the fuseholder in the battery box.

PMM

[peterpixel]

Thanks for the info PMM this gets more interesting by the minute.There is no fuseholder in the battery box, however the battery box cover which is a metal plate and not the usual moulded bakelite type has an AVO label on the inside showing a 1 amp fuse position and a spare fuse position.The 15 volt battery on the label is also in the same orientation as the 1.5 volt cell. Perhaps this is a hybrid occurring at the changeover of MKII / III or the cover has just been taken from another model. Do you know of any other differences between the MKII and III? I look forward to the next installment. Peter

[The Philpott]

It is possible for a MkII battery box to be used in a MkIII meter. (I have done it myself!)
The metal battery box LID is normal for a MKIII....earlier ones (i think)....may have had either metal or bakelite lids.

Nothing wrong with a 'Bitzer'!

If i remember correctly, the MkIII has a germanium based rectifier and the MkII a copper oxide rectifier. The instruction plate on the rear mentions this as it was considered a significant improvement.

Dave

[Pamphonica]

I just finished tidying up a 1951 High Resistance Avometer. The precursor to the Model 8. A gap in my collection filled.
It came as a very dirty and rattling heap, from Ebay. The rattle turned out to be a completely loose movement, and evidence of some restorative soldering, and a broken swamp resistor bobbin. Sadly, once put back together, it turns out to have an open-circuit movement. At least it now looks very smart again!

The serial number puts it as the youngest on the 3rd edition Avo list. But the serial number date puts it just before the last two, so that's an anomaly. Inside, the movement and the zero adjuster are is marked 2811 and 1951, so it is original, I suspect.

Model: High Resistance (model 2 - HR2)
Serial: 2811-B-0150 (October 1950)

-Jeremy

[Superscope]

Hi Peter,

There are a number of problems knowing what is/was original and
what is/was a modification later in the life of the meter.

Avo were renowned for using old/Different Stock parts on their meters,
when the need arose.

Your meter is a very late Mk III so it is quite possible Avo just decided to use up some old stock
Battery Boxes, before that style became completely obsolete.

The last Mk III left the factory around November 1969.
The Mk IV launched around December that year and used an entirely different Battery Bay.


Also, as Dave has pointed out, the Battery Box may just have been changed out.

This is an on going problem for Historical re-search, as many of the Avo 8 Parts are
interchangable between Marks (and Models) , and were (and still are) often swapped about.
It's difficult to rule anything out with Avo meters.

Does your Meter front Panel have a Blank Ident, or is the Circular Moulding missing completely?

I suspect you have a very late Meter and the Battery Bay has been changed
at some point probably due to a serious Battery Leakage problem.


Ian

[Superscope]

Ref Post # 2785

Hi Jeremy,

Can you confirm that HR2 Serial Number ?
You said 0150, but wrote October 1950.

I have a problem fitting 2811 in the HR sequences.
It is the highest HR2 Serial Number, but the Date Code doesn't fit.
I would expect 2811 to be somewhere around March/April 1951
which would make it the youngest on record, but of course the
Date Code throws this out the window!
As you have already noticed.

There seemed to be approximately 100 HR Model Avometers produced
per Month, from April 1948 to February 1951.



Incidently, there was a 4th Edition of the survey published.



Ian

[Pamphonica]

Sorry, serial is
2811-B-1050
2811 is marked on rear of dial and on the brass zero adjuster in the case, so no real likelihood of movement substitution
Which still causes problems with ordering!
The inside is clearly marked 1951.
Photos attached of dial plate removed during repair, and markings inside.
-Jeremy

[Pamphonica]

Missed 4th Edition of the survey. Must try to find it. We really need to ask the mods to put a link on the very first page to the latest survey post. By the way, the 3rd Edition HR section states that the HR was a DC only instrument. Actually it's not; it's dc and ac. It just has very odd switching compared to the later and more logical Model 8
Jeremy

[Superscope]

Hi Jeremy,

Yes, even for me, the Survey is a learning Curve.
I didn't know much about the Model HR when I wrote the 3rd Edition.
I had to go by what others had said.

The 4th Edition, was updated quite a bit.
It can be found on Page 120 Post # 2397

I have only recently aquired a Model HR myself.
But can't get it open for repair, so will probably
start a Model HR thread soon.



A 5th Edition Survey is in the Works, but as nobody has asked about it,
I've had it on the back burner as they say.


Ian

[The Philpott]

Yes, the HR Avometer has AC volts facility but is marked out by the lack of a transformer and therefore lack of AC current facility.

I notice the scale plate for the Model 2 HR meter is quite unlike my Model 1..My low resistance range has 'zero' at the LOW end of the scale, the Model 2 is more conventional.
This could be because the Model 1 measures the voltage across the resistance, as opposed to the current across the resistance....?

-This puts the mockers on me offering Jeremy money for his scale plate! (The red legends on mine are very badly faded)

I did actually use the Low ohms range this week, for checking old 13amp extension reels. (350 millohms for 20 metres of 1.25mm2 copper, if the pins are nicely polished.)

Dave

[pmmunro]

There seem to be a disproportionately high number of Avometer HR movements which are open circuit. Other than the HR Minor, it was the first 20,000 ohms per volt instrument which implies much finer wire was used for the moving coil than in previous Avometers.

Whatever the cause, it seems to have been cured in the Model 8, because open circuit movements are rare. One significant difference is that the acceleration cut-out is not used in the Model 8, although the toothed disc in front of the concentrator was still fitted.

PMM

[Sinewave]

I've got loads to add since the last survey, I'd better do an audit of my collection.

Will the top contributors list see a return?

[peterpixel]

Hi Ian, back to my mysterious MK II or III. Mine has a blank ident above the cut out, where normally one would see MK II or III etc. I had a look on Richardsradios and the photo of the rear of the MK III is identical to mine and doesn't include the copper oxide rectifier missing on mine. Mine does have the VA1039 thermistor above the magnet. What I haven't been able to locate are the OA95 diodes although there is one OA type adjacent to the VA1039. They have got to be lurking in there somewhere as the unit works fine on AC. Thank you Dave (The Philpott) for pointing out the copper oxide/germanium changeover. Just to complicate matters my backplate mentions the use of copper oxide but not germanium. I think as Ian has stated that this is a late model and AVO were using up materials in stock at the time. Thanks for your efforts in trying to nail this one. Peter.

[pmmunro]

Peter,

The varistor confirms that the movement in your meter is a MkIII type. the magnet blocks should be unpainted, whereas the Mk II type would be painted red. (The Mk I type are also unpainted but thicker than the later ones). This however does not mean that the meter started out as a Mk III.

I have an HR Avometer which has a Mk III movement which appears to have been from a factory repair.

Much as we would like everything to be historically consistent, the original users would only have been concerned with having a working meter using available parts. For local repairs, this could have even been without regard for which front panel went with which case.

PMM

[peterpixel]

Good morning PMM and thanks for the response. I don't think I will lose any sleep over worrying about the meters parentage although I just wish I could remember where in my career this one appeared. Thanks for the input. Peter.

[Superscope]

For those interested,

The Type D Meter recently advertised, sporting a Model 7
Front Panel was dated October 1940.

The Listing has gone, so I assume somebody has bought it.
It wasn't me by the way!

Anybody on here maybe, willing to own up to it?


Very odd having that Front Panel, since it would have made
far more sense for ACWEECO to have used it on a Model 7.
Since Model 7's seem to have all been using Universal Front Panels
by this Time.




Ian

[Aitor Eneko]

Thanks

I did not buy it

[The Philpott]

Me neither! I don't think Model D production had got into full swing in late 1940, the bulk of the survivors seem to be 1944-45. They may have been grabbing bits and pieces from here and there to fulfil the early orders. It could of course be a shadow factory unit, but i would think these started up later than 1940. I have a Model 7 from 1939 which was put together rather shoddily. It has an aluminium back box. They could originate from the same production line-perhaps.

Dave

[Barnmead]

Have just acquired a model5 serial 38-7445 it is in quite nice condition complete with leather case and perished leads, probes and spare fuses. It seems to have faults on highest voltage ranges AC and DC and two of the ohms ranges. I have yet to investigate further but will update on progress when time permits.